Cortana’s and Master Chief’s voices in MCC can’t be heard in Halo 4 campaign when the console language is not set to English. Seems it refers to non-existent voice files or files are incorrectly referenced.
I can’t say 100%, but I have a feeling that the sound scheme is not full and it’s not only voices that are missing.
The only workaround to this is to switch the whole console to English. It also forces me to change location to some other than my real location, but that’s an Xbox bug, not yours.